Evacuated Tube Solar Water Heating

Learn about the most efficient way to use the sun to heat water

Solar Water Heating (1) has been used for hundreds if not thousands of years to heat water. With advances in technology solar water heating systems have become more and more efficient, with Evacuated Tube Solar Water Heatings offering efficiencies of well over 90%. That means that more than 90% of the sun's energy landing on a surface is converted into heat which can be used to heat water. This is also one of the cheapest renewables, with costs starting from pennies per Watt required comparing to pounds per Watt for PV Solar (2) and Wind Turbine (3) power generation.

Solar water heating evacuated tube schematic

Vacuum or Evacuated Tubes are made from glass - typically ultra-strong and heat resistant Pyrex with a double wall construction. The glass on the inner tube is coated on its outer surface with an absorbant coating, and on its inner surface with a reflective coating. Inside each tube all air is removed making a vacuum and a copper heat pipe is located through the centre of the tubes. Most of the infra-red radiation (i.e heat) from the sun is absorbed by this sealed heat pipe which contains an anti-freeze type liquid.

As heat rises, hot vapours from the antifreeze rise up to the top of the heat pipe where its copper tip connects with a header pipe through which more antifreeze flows. This hot antifreeze is then pumped through pipes inside the hot water tank with the end result that the water gets hotter and the antifreeze cooler. The antifreeze then continues its journey around the system and back out to the solar water heater to be reheated.

The copper at the tip of the heat tube can reach well over 200 degrees easily heating water to 90 degrees celcius on hot days and to 60 degrees celcius even in the winter. This simple system is completely sealed and needs minimal maintenance over its 20+ years life.

The advantage of using evacuated tubes is that they will work even during the coldest winter months unlike old style Flat Plate Solar Collectors. The vacuum prevents the heat tube from being cooled much by the ambient temperature which can be well below freezing, and so winter sun can easily heat water to 50+ degrees even in the depths of the coldest season. Even if it is very cloudy and very cold, enough sunlight gets through to keep the tubes well above freezing and so they will be still be pre-heating the water which can then be heated further by a standard immersion heater or gas burner reducing the costs of heating the water.

Evacuated tube solar water heating system schematic

The fitting of a Solar Water Heating system using evacuated tubes can be carried out by any able DIY enthusiast with basic plumbing skills. The solar tubes are usually put on modules of 10 or 20 tubes which are then connected via insulated copper piping to a suitable hot water cylinder. Pictured above is a schematic showing the installation of a modular evacuated tube solar water heating system.

Buy an Evacuated Tube Water Heating System

Until recently it was difficult for the amateur to get their hands on an economical array of evacuated tubes in order to install a DIY solar water heating system. That has now all changed thanks to eBay (4). Click here to search eBay for Evacuated Tube (5) now to view a list of what's available for sale today.

Web Link References

(1) http://www.reuk.co.uk/Introduction-to-Solar-Water-Heating.htm
(2) http://www.reuk.co.uk/How-Do-PV-Solar-Panels-Work.htm
(3) http://www.reuk.co.uk/wind.htm
(4) http://rover.ebay.com/rover/1/710-53481-19255-0/1?type=1&campid=5336029681&toolid=10001&customid=
(5) http://rover.ebay.com/rover/1/710-53481-19255-0/1?type=3&campid=5336029681&toolid=10001&customid=&ext=evacuated+tube&satitle=evacuated+tube

Article from REUK.co.uk:
http://www.reuk.co.uk/Evacuated-Tube-Solar-Water-Heating.htm
Published: 21st July 2008
© REUK 2009